Optical device and method of making

ABSTRACT

An optical device and method is disclosed for forming the optical device within the wide-bandgap semiconductor substrate. The optical device is formed by directing a thermal energy beam onto a selected portion of the wide-bandgap semiconductor substrate for changing an optical property of the selected portion to form the optical device in the wide-bandgap semiconductor substrate. The thermal energy beam defines the optical and physical properties of the optical device. The optical device may take the form of an electro-optical device with the addition of electrodes located on the wide-bandgap semiconductor substrate in proximity to the optical device for changing the optical property of the optical device upon a change of a voltage applied to the optional electrodes. The invention is also incorporated into a method of using the optical device for remotely sensing temperature, pressure and/or chemical composition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 60/647,678 filed Jan. 26, 2005. All subject matter set forth inprovisional patent application Ser. No. 60/647,678 is herebyincorporated by reference into the present application as if fully setforth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to optical devices and more particularly to animproved apparatus and method for the fabrication of optical devices andelectro-optical devices within a wide-bandgap semiconductor substrate bydirecting a thermal energy beam onto the wide-bandgap semiconductorsubstrate.

2. Description of the Related Art

Conventional semiconductors such as silicon have been used for variouselectrical, electronic and electro-optical devices. Conventionalsemiconductors are limited to operating temperatures below 250° C., dueto the narrow band gap and poor thermal stability. There has been anincreasing need to extend the limits of sensors for high temperature andharsh environments operations.

Wide-bandgap semiconductors have many advantages over conventionalsemiconductors such as silicon. One wide-bandgap semiconductor suitablefor replacing conventional silicon-based devices is silicon carbide(SiC). The bandgap of 6H—SiC silicon carbide (SiC) is around 3 eV [2]which is about two times greater than the bandgap of silicon.Furthermore, silicon carbide (SiC) supports very high breakdown field,3-5 MV/cm. The high sublimation temperature about 2700° C. and extremelylow intrinsic carrier concentration allows silicon carbide (SiC) tooperate at elevated temperatures. The dependence of intrinsic carrierconcentration on temperature causes threshold voltage-shift and leakagecurrent, resulting in device degradation and latchup phenomenon. Thestrong covalent bonds between Si and C yield high frequency latticevibrations, generating high energy optical phonons (100-120 meV), thatlead to a high saturation drift velocity (2×10′ cm/s) and excellentthermal conductivity (490 W/m·K).

Silicon carbide (SiC) is the only wide bandgap semiconductor that hassilicon dioxide as its native oxide analogous to silicon. Siliconcarbide (SiC) is potentially superior to other compound semiconductorssince silicon carbide (SiC), allows the creation of a metal oxide.

Silicon carbide (SiC) is a promising semiconductor material for opticaldevices, particularly mirrors and lenses because of its low thermalcoefficient of expansion, hardness (and hence good polishability), highthermal conductivity (350-490 Wm⁻¹K⁻¹) and chemical stability in hostileenvironments.

Doping is a challenge for silicon carbide (SiC) due to the hardness,chemical inertness and the low diffusion coefficient of most impuritiesof silicon carbide (SiC). Current doping techniques for silicon carbide(SiC) device fabrication include epilayer doping and ion implantation.

Epilayer doping is introduced during chemical vapor deposition (CVD)epitaxial growth. Nitrogen (N) or phosphorous (P) are used as a dopingmaterial for n-type silicon carbide (SiC) whereas aluminum (Al) andboron (B) are used as a doping material for p-type silicon carbide(SiC). Vanadium (V) is used as a doping material for semi-insulatingsilicon carbide (SiC).

Ion implantation is the most common doping technique used for siliconcarbide (SiC). However, ion implantation generates implantation-induceddefect centers in the silicon carbide (SiC) and therefore, highannealing temperatures are required to remove this damage and toelectrically activate the dopants. Some defects remain in siliconcarbide (SiC) for up to 1700° C. annealing temperatures. Annealing atthese high temperatures can cause severe surface damage due to silicon(Si) sublimation and redistribution.

A laser conversion technology for wide bandgap semiconductors includingsilicon carbide (SiC) is disclosed in the prior inventions of NathanielR. Quick. Discussion of wide bandgap materials and the processingthereof are set forth in U.S. Pat. No. 5,145,741; U.S. Pat. No.5,391,841; U.S. Pat. No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat.No. 6,025,609; U.S. Pat. No. 6,054,375; U.S. Pat. No. 6,271,576 and U.S.Pat. No. 6,670,693 are hereby incorporated by reference into the presentapplication.

The above prior inventions of Nathaniel R. Quick disclose thefabrication of various electrical and electronic devices. The presentinvention expands the prior inventions of Nathaniel R. Quick byfabricating optical devices and electro-optical devices in a widebandgap semiconductor through a laser conversion process.

Therefore, it is an object of the present invention to provide opticaldevices and electro-optical devices and a method of making through alaser conversion process of a wide bandgap semiconductor.

It is an object of the present invention to provide an optical deviceand method of making by directing a thermal energy beam onto a selectedportion of the wide-bandgap semiconductor substrate for changing anoptical property of the selected portion to form the optical device.

Another object of the present invention is to provide an optical deviceand method of making an optical device on the surface of a wide-bandgapsemiconductor substrate or within a wide-bandgap semiconductorsubstrate.

Another object of the present invention is to provide an optical deviceand method of making an optical device for defining a shape of theoptical device in the wide-bandgap semiconductor substrate.

Another object of the present invention is to provide an optical deviceand method of making an optical device including the formation ofelectrodes on a wide bandgap semiconductor adjacent to the opticaldevice for forming an electro-optical device.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed as being merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be obtained bymodifying the invention within the scope of the invention. Accordinglyother objects in a full understanding of the invention may be had byreferring to the summary of the invention, the detailed descriptiondescribing the preferred embodiment in addition to the scope of theinvention defined by the claims taken in conjunction with theaccompanying drawings.

SUMMARY OF THE INVENTION

The present invention is defined by the appended claims with specificembodiments being shown in the attached drawings. For the purpose ofsummarizing the invention, the invention relates to an improved opticaldevice, comprising a wide-bandgap semiconductor substrate having a firstoptical property. An optical device is defined within the wide-bandgapsemiconductor substrate having a second optical property different fromthe first optical property.

In another embodiment of the invention, the invention is incorporatedinto an electro-optical device, comprising a wide-bandgap semiconductorsubstrate having a first optical property. An optical device is definedwithin the wide-bandgap semiconductor substrate having a second opticalproperty. A first and a second electrode are located in proximity to theoptical device for changing the second optical property upon a change ofa voltage applied to the first and second electrodes.

The invention is also incorporated into the method for making an opticaldevice within a wide-bandgap semiconductor substrate. The methodcomprises the steps of providing a wide-bandgap semiconductor substrate.A thermal energy beam is directed onto a selected portion of thewide-bandgap semiconductor substrate for changing an optical property ofthe selected portion to convert the selected portion of the wide-bandgapsemiconductor substrate into the optical device.

The invention is also incorporated into the method for making anelectro-optical device within a wide-bandgap semiconductor substrate.The method comprises the steps of providing a wide-bandgap semiconductorsubstrate. A first thermal energy beam is directed onto a first selectedportion of the wide-bandgap semiconductor substrate for changing anoptical property of the first selected portion to convert the firstselected portion of the wide-bandgap semiconductor substrate into theoptical device. A second thermal energy beam is directed onto a secondselected portion of the wide-bandgap semiconductor substrate forchanging an electrical property of the second selected portion toconvert the second selected portion of the wide-bandgap semiconductorsubstrate into the electrical device.

The invention is also incorporated into the method of measuring atemperature of a remote location. The method of measuring temperaturecomprises providing a wideband gap semiconductor sensor having anoptical property that varies with temperature. The wideband gapsemiconductor sensor is positioned in the remote location. The widebandgap semiconductor sensor is irradiated with an interrogating laser beam.The reflected radiation from the wideband gap semiconductor sensor isdetected and processed to determine the temperature of the remotelocation.

The invention is also incorporated into the method of measuring pressureat a remote location. The method of measuring pressure comprisesproviding a wideband gap semiconductor sensor having an optical propertythat varies with applied pressure. The wideband gap semiconductor sensoris positioned in the remote location with the pressure of the remotelocation applied to a surface of the wideband gap semiconductor sensor.The wideband gap semiconductor sensor is irradiated with aninterrogating laser beam. The reflected radiation from the wideband gapsemiconductor sensor is detected and processed to determine the pressureat the remote location.

The invention is also incorporated into the method of measuring achemical composition at a remote location. The method of measuring thechemical composition comprises providing a wideband gap semiconductorsensor having an optical property that varies with chemical composition.The wideband gap semiconductor sensor is positioned in the remotelocation with the chemical composition of the remote location applied toa surface of the wideband gap semiconductor sensor. The wideband gapsemiconductor sensor is irradiated with an interrogating laser beam. Thereflected radiation from the wideband gap semiconductor sensor isdetected and processed to determine the chemical composition at theremote location.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription that follows may be better understood so that the presentcontribution to the art can be more fully appreciated. Additionalfeatures of the invention will be described hereinafter which form thesubject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a side view of an air-tight chamber with a thermal energy beamimpinging on a wide-bandgap semiconductor substrate for forming a firstembodiment of an optical device;

FIG. 2 is an enlarged isometric view of the first embodiment of theoptical device formed on a surface of the wide-bandgap semiconductorsubstrate of FIG. 1;

FIG. 3 is a side view of an air-tight chamber with a concentratedthermal energy beam impinging on a wide-bandgap semiconductor substratefor forming a second embodiment of an optical device;

FIG. 4 is an enlarged isometric view of the second embodiment of theoptical device formed within the wide-bandgap semiconductor substrate ofFIG. 3;

FIG. 5 is a reproduction of a photograph of a section of a wide-bandgapsemiconductor substrate with the optical device embedded therein;

FIG. 6 is an enlarged isometric view of third embodiment of an opticaldevice formed within the wide-bandgap semiconductor substrate;

FIG. 7 is an enlarged isometric view of fourth embodiment of anelectro-optical device formed within the wide-bandgap semiconductorsubstrate;

FIG. 8 is a graph of transmission as a function of wavelength for aseries of applied voltages to the electro-optical device of FIG. 7;

FIG. 9 is an enlarged isometric view of a fifth embodiment of anelectro-optical device formed in a specific shape within thewide-bandgap semiconductor substrate;

FIG. 10 is a sectional view along line 10-10 in FIG. 9;

FIG. 11 is a sectional view similar to FIG. 10 with a voltage applied tothe electro-optical device;

FIG. 12 is a diagram of a process of measuring the temperature of remotelocation with a wide-bandgap sensor;

FIG. 13 is a diagram of a process of measuring the pressure and/orcomposition of remote location with a wide-bandgap sensor;

FIG. 14 is a graph illustrating the reflected power for a sample A as afunction of temperature from 27° C. to 750° C. for a zero degree (0°)and a forty-five degree (45°) incidence angle;

FIG. 15 is a graph illustrating the reflected power for sample B as afunction of temperature from 27° C. to 750° C. for a zero degree (0°)and a forty-five degree (45°) incidence angle;

FIG. 16 is a graph illustrating a typical oscillatory reflected powerprofile commonly referred to as a complementary Airy pattern showing thephase angles between the adjacent branches of the oscillations;

FIG. 17 is a graph of the refractive index for sample A and B, from 27°C. up to 750° C., for 0° and 45° incidence angle;

FIG. 18 is a graph illustrating the concentration depth profiles ofAluminum and Nitrogen measured with SIMS for sample A;

FIG. 19 is a graph illustrating the concentration depth profiles ofAluminum and Nitrogen measured with SIMS for sample B;

FIG. 20 is a graph illustrating the reflectivity plot for sample A andB, as a function of temperature from 27° C. up to 750° C. for 0° and 45°incidence angle;

FIG. 21 is a graph illustrating the thermo optic coefficient for sampleA and B from 27° C. up to 750° C. for 6H silicon carbide (SiC) for 0°and 45° incidence angle and literature value for 6H silicon carbide(SiC) at 1.5 micro meter wavelength;

FIG. 22 is a graph illustrating the reflected power for laser-metallizedsample as a function of temperature for normal incidence of a He—Nelaser beam of power incident on a substrate the wafer is 6.7 mW;

FIG. 23A is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 14.7 psi;

FIG. 23B is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 100 psi;

FIG. 23C is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 200 psi;

FIG. 23D is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 400 psi;

FIG. 24A is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 14.7 psi;

FIG. 24B is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 100 psi;

FIG. 24C is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 200 psi;

FIG. 24D is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 400 psi;

FIG. 25 is a graph of the refractive index of silicon carbide sensorwhen exposed to nitrogen as a function of temperature at pressures of14.7 psi, 100 psi, 200 psi and 400 psi;

FIG. 26 is a graph of the refractive index of silicon carbide sensorwhen exposed to argon as a function of temperature at pressures of 14.7psi, 100 psi, 200 psi and 400 psi;

FIG. 27 is a graph of the refractive index of a composite layer uponexposure to Nitrogen as a function of temperature at pressures of 14.7psi, 100 psi, 200 psi and 400 psi;

FIG. 28 is a graph of the refractive index of a composite layer uponexposure to argon as a function of temperature at pressures of 14.7 psi,100 psi, 200 psi and 400 psi;

FIG. 29A is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 14.7 psi;

FIG. 29B is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 100 psi;

FIG. 29C is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 200 psi;

FIG. 29D is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 400 psi;

FIG. 30A is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 27° C.;

FIG. 30B is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 100° C.;

FIG. 30C is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 200° C.; and

FIG. 30D is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 300° C.

Similar reference characters refer to similar parts throughout theseveral Figures of the drawings.

DETAILED DISCUSSION

FIG. 1 is a side view of an apparatus 5 for forming first embodiment ofan optical device 10 on a wide-bandgap semiconductor substrate 20. Thewide-bandgap semiconductor substrate 20 is shown located in an air-tightchamber 30. The chamber 30 has an inlet valve 31 and an outlet valve 32connected to the side wall of the chamber 30. The inlet valve 31 and theoutlet valve 32 permit the injection and removal of gases into and fromair-tight chamber 30. The chamber 30 includes an airtight transmissionwindow 34. The chamber 30 is disposed on a support member 36 forming anairtight seal therewith.

FIG. 2 is an enlarged isometric view of the wide-bandgap semiconductorsubstrate 20 shown in FIG. 1. The wide-bandgap semiconductor substrate20 defines a first and a second side 21 and 22 and a peripheral edge 23.Although the wide-bandgap semiconductor substrate 20 is shown as asquare, the present invention is not limited by the physicalconfiguration of the wide-bandgap semiconductor substrate 20 as shownherein.

A thermal energy beam 40 is shown emanating from a source 42 and passingthrough the airtight transmission window 34 to impinge on the firstsurface 21 of the wide-bandgap semiconductor substrate 20. In oneexample, the thermal energy beam 40 is a beam of charged particles suchas a beam of electrons or a beam of ions. In another example, thethermal energy beam 40 is a beam of electromagnetic radiation such as alaser beam. Examples of a suitable source of the laser beam include aNd:YAG laser, a frequency double 2ω Nd:YAG laser or an Excimer laser.

The optical device 10 is shown as a portion of the wide-bandgapsemiconductor substrate 20 formed by causing relative movement betweenthe wide-bandgap semiconductor substrate 20 and the thermal energy beam40. The thermal energy beam 40 impinges on the wide-bandgapsemiconductor substrate 20 to create the optical device 10 within thewide-bandgap semiconductor substrate 20. The thermal energy beam 40 isscanned in two dimensions across the first surface 21 of the widebandgap semiconductor substrate 20 to form the optical device 10. In thisexample, the first surface 11 of the optical device 10 is coincidentwith the first surface 21 of the wideband gap semiconductor substrate 20with the remainder of the optical device 10 including the second surface12 and the peripheral surface 13 being embedded within the wideband gapsemiconductor substrate 20.

The wide-bandgap semiconductor substrate 20 may be formed as a monolithor a thin film substrate having suitable properties for forming theoptical device 10 in the wide-bandgap semiconductor substrate 20.Preferably, the wide-bandgap semiconductor 20 has a bandgap greater than2.0 electron volts. In one example, the wide-bandgap semiconductor 20 isselected from the group IV of the periodic table and having a bandgapgreater than 2.0 electron volts. In a more specific example of theinvention, the wide-bandgap semiconductor 20 is essentially a singlecrystal structure.

In still a more specific example of the invention, the wide-bandgapsemiconductor 20 may be a single crystal compound. The elements of thesingle crystal compound selected are from the group III and the group Vof the periodic table and having bandgap greater than 2.0 electronvolts. Preferably, one element of the compound has a higher meltingpoint element than the other element of the compound. Specific examplesof the wide-bandgap semiconductor compound are selected from the groupconsisting of Aluminum Nitride, Silicon Carbide, Boron Nitride, GalliumNitride and diamond.

The inlet valve 31 and the outlet valve 32 in the side wall of thechamber 30 enables the introduction and removal of gases while thethermal energy beam 40 impinges on the wide-bandgap semiconductorsubstrate 20. Preferably, doping gases are introduced and removed fromthe air-tight chamber 30 during the thermal conversion process. Theintroduction and removal of doping gases from the air-tight chamber 30changes the characteristics of the optical device 10 during the thermalconversion process.

FIG. 3 is a view similar to FIG. 1 illustrating the air-tight chamber 30with a concentrated thermal energy beam 46 impinging on a secondwide-bandgap semiconductor substrate 20A for forming a second embodimentof an optical device 10A. In this embodiment of the invention, thethermal energy beam 40 is passed through an optical element 44 shown asthe lens to provide a concentrated thermal energy beam 46 converging ata focal point 48. The optical element 44 is located relative to thewideband gap semiconductor substrate 20A to focus the focal point 48 ofthe concentrated thermal energy beam 46 within the interior of thewideband gap semiconductor substrate 20A.

FIG. 4 is an enlarged isometric view of the second embodiment of theoptical device 10A formed within the wide-bandgap semiconductorsubstrate 20A of FIG. 3. A two-dimensional movement of the concentratedthermal energy beam 46 creates the optical device 10A to be totallywithin the wideband gap semiconductor substrate 20A.

The concentrated thermal energy beam 46 is adjusted such that thenon-concentrated thermal energy beam 46 impinging upon the firstsurfaced 21A of the wide-bandgap semiconductor substrate 20A isinsufficient in intensity to convert the wideband gap semiconductorsubstrate 20A into the optical device 10A. The intensity of the focalpoint 48 of the concentrated thermal energy beam 46 is sufficient toconvert the wideband gap semiconductor substrate 20A into the opticaldevice 10A. The optical device 10A is formed totally within the widebandgap semiconductor substrate 20A to protect optical device 10A by thesurrounding wideband wideband gap semiconductor material 20A.

FIG. 5 is a reproduction of a photograph of a section of thewide-bandgap semiconductor substrate with an optical device embeddedtherein. The photograph is representative of the wide-bandgapsemiconductor substrate 20A with the optical device 10A shown in FIGS. 3and 4.

FIG. 6 is an enlarged isometric view of the third embodiment of theoptical device 10B formed within the wide-bandgap semiconductorsubstrate 20B. A two-dimensional movement of the concentrated thermalenergy beam 46 creates the optical device 10B to be formed totallywithin the wideband gap semiconductor substrate 20B.

In this embodiment of the invention, the second surface 12B of theoptical device 10B is coincident with the second surface 22B of thewideband gap semiconductor substrate 20B with the remainder of theoptical device 10B including the first surface 11B and the peripheralsurfaces 13B being embedded within the wideband gap semiconductorsubstrate 20B.

FIG. 7 is an enlarged isometric view of fourth embodiment of anelectro-optical device 10C formed within the wide-bandgap semiconductorsubstrate 20C. The wide-bandgap semiconductor substrate 20C defines afirst and a second side 21C and 22C and a peripheral edge 23C. In thisexample, the first surface 11C of the optical device 10C is coincidentwith the first surface 21C of the wideband gap semiconductor substrate20C with the remainder of the optical device 10C including the secondsurface 12C and the peripheral surface 13C being embedded within thewideband gap semiconductor substrate 20C.

A first and a second electrode 51 and 52 are interconnected to opposedsections 13C′ and 13C″ of the peripheral edge 13C of the optical device10C. The first and second electrodes 51C and 52C are electricallyconnected to a first and second connector 61C and 62C. Preferably, thefirst and second electrodes 51C and 52C and the first and secondconnectors 61C and 62C are formed by the thermal conversion of thewide-bandgap semiconductor substrate 20C. The thermal conversion processfor forming the first and second electrodes 51C and 52C and the firstand second connectors 61C and 62C in the wide-bandgap semiconductorsubstrate 20C is set forth in my U.S. Pat. No. 5,145,741; U.S. Pat. No.5,391,841; U.S. Pat. No. 5,793,042; U.S. Pat. No. 5,837,607; U.S. Pat.No. 6,025,609; U.S. Pat. No. 6,054,375; U.S. Pat. No. 6,271,576 and U.S.Pat. No. 6,670,693.

An incident wave 71C enters into the first side 21C of the wide-bandgapsemiconductor substrate 20C and passes through the electro-opticaldevice 10C to exit as an emerging wave 72C from the second side 22C ofthe wide-bandgap semiconductor substrate 20C. The emerging wave 72Cexiting from the second side 22C of the wideband gap semiconductorsubstrate 20C is reduced in amplitude relative to the incident wave 71Centering into the first side 21C of the wideband gap semiconductorsubstrate 20C.

FIG. 8 is a graph of percent of transmission as a function of wavelengthfor the electro-optical device 10C of FIG. 7. The graphs illustrate thepercent of incident wave 71C entering into the first side 21C of thewide-bandgap semiconductor substrate 20C that exits as an emerging wave72C from the second side 22C of the wideband gap semiconductor substrate20C.

The curve labeled 5V illustrates the percent of incident wave 71C thatexits as the emerging wave 72C with a 5 volt bias applied between thefirst and second electrodes 51C and 52C.

The curve labeled 7V illustrates the percent of incident wave 71C thatexits as the emerging wave 72C with a 7 volt bias applied between thefirst and second electrodes 51C and 52C. The curve labeled 9Villustrates the percent of incident wave 71C that exits as the emergingwave 72C with a 9 volt bias applied between the first and secondelectrodes 51C and 52C. The series of curves 5V, 7V and 9V illustratethe percent of incident wave 71C that exits as an emerging wave 72C maybe varies by the voltage applied to the first and second electrodes 51Cand 52C.

FIG. 9 is a fifth embodiment of the invention illustrating anelectro-optical device 10D formed in the wideband gap semiconductorsubstrate 20D. In this example, the optical device 10D is shown as aconvex lens located within the wideband gap semiconductor substrate 20D.The shape of the lens 10D is formed concurrently with the conversion ofthe material of the wideband gap semiconductor substrate 20D into theoptical device 10D. The shape of the optical device 10D may be formed bya number of methods including a three-dimensional movement of thethermal energy beam 40 and/or varying the intensity and/or the speed ofmovement of the thermal energy beam 40 impinging upon the wideband gapsemiconductor substrate 20D. It should be appreciated by those skilledin the art that the convex lens 10D illustrated in FIG. 9 is merely anexample of one type or shape of an optical device which may be formed bythe present invention. It should be further appreciated by those skilledin the art that numerous other shapes, sizes and alterations of theoptical device 10D may be formed in accordance with the practice of thepresent invention.

FIG. 10 is a sectional view along line 10-10 in FIG. 9 furtherillustrating the shape of the optical device 10D. The incident wave 71Denters into the first side 21D of the wide-bandgap semiconductorsubstrate 20D and exits as an emerging wave 72D from the second side 22Dof the wideband gap semiconductor substrate 20D after passing throughthe optical device 10D. The emerging wave 72D is shown symbolicallyexiting from the second side 22D to be parallel to the incident wave 71Denters into the first side 21D of the wide-bandgap semiconductorsubstrate 20D.

FIG. 11 is a sectional view similar to FIG. 10 with a voltage applied tothe electro-optical device 10D. The voltage applied to the first andsecond electrodes 51D and 52D alters the refraction index of theelectro-optical device 10D. The emerging wave 72D is shown symbolicallyexiting from the second side 22D to be refracted or altered in directionrelative to the incident wave 71D entering into the first side 21D ofthe wide-bandgap semiconductor substrate 20D.

EXAMPLE I Laser Synthesis of Optical Phases (Structures)

-   -   6H—SiC (single crystal with (0001) Si-face semi-insulating)        wafers, 443 μm thick, were placed in a controlled environment        and then irradiated with a scanning laser beam. Laser        metallization surface and embedded metal-like conductive tracks        were produced in both n-type and p-type SiC substrates by the        laser direct write technique using inert ambient (Ar and He).        Laser metallization is the conversion of a wide bandgap        semiconductor to a conductor with a resistivity less than 10⁻²        ohm-cm without the addition of metal. Nanosecond-pulsed Nd:YAG        (λ=1064 and 532 nm) and excimer (λ=193, 248 and 351 nm) lasers        are used. These lasers are capable of laser metallization of        insulating and semiconducting crystalline or polycrystalline        wide-bandgap semiconductors necessary to fabricate and produce        the various optical and electro-optical devices taught by the        invention.    -   Laser doping experiments were conducted using a Nd:YAG laser of        wavelength 1064 nm that can be operated in both continuous wave        (CW) and Q-switched modes. For the Q-switched mode, the pulse        repetition rate was varied from 2 to 35 kHz. The sample was        placed inside a gas tight chamber where it was simultaneously        irradiated with the laser and exposed to a dopant-containing        ambient. Laser-doped tracks were formed on the sample surface by        moving the chamber on a stepper motor-controlled translation        stage. The height of the chamber was controlled manually through        an intermediate stage to obtain different laser spot sizes on        the SiC substrate surface. Nitrogen and Trimethyaluminum (TMA)        were used as n-type and p-type dopant gases respectively. The        sample was placed in nitrogen of pressure 30 psi for n-type        doping. For p-type doping, TMA was separately heated in a        bubbler until it evaporated and then a carrier gas Ar was passed        through the bubbler to deliver the TMA vapor to the laser doping        chamber through a gas tight tube. TMA decomposes at the        laser-heated substrate surface producing Al atoms, which        subsequently diffuse into the substrate. The SiC substrate was        kept at room temperature before laser irradiation in all the        experiments.

TABLE 1 Laser Processing Parameters. Pulse Beam Laser repeti- spot Scan-process- Pulse tion Focal dia- Laser ning Irra- ing energy rate lengthmeter fluence speed diation region (mJ) (kHz) (mm) (μ) (J/cm²) (mm/s)passes n-type 4.7 3 150 300 6.65 1 1 zone p-type 5.5 2 150 300 7.75 1 1zone Laser 4.7 3 150 300 6.65 1 1 metal- lization zone

Dopant depth profiles were obtained using secondary ion massspectroscopy (SIMS) with Cs and O2+ sources forming the primary beam.The energy and current of the primary beam were 8 keV and 1 μArespectively, and it was rastered over an area of 200 μm×200 μm of thelaser-doped sample. The dopant depth was calculated from the sputteringrate and time.

Reflectivity and transmission of the as-received, laser metallizationand laser doped wafers were measured. These data are used to calculatethe optical constants.

Laser metallization of SiC without metal deposition relies on theability of a laser beam to locally change the stoichiometry of SiCthrough intense photonic and thermal energy coupling between the beamand the substrate. Pulsed laser irradiation changes the stoichiometry bytransforming SiC into either Si-rich or C-rich phases, depending on thechosen processing parameters.

Laser doping has been used to dope both n-type (nitrogen) and p-type(aluminum) dopants in SiC. For n-type doping nitrogen gas was used as adopant precursor. SIMS (Secondary Ion Mass Spectroscopy) is used toobtain doping concentration profiles for the laser doping processingparameters defined in Table 1. The nitrogen concentration decreasesslowly from a wafer surface concentration of approximately 1021 cm-3 to1.5×1020 cm-3 at a depth of 3 μm. Curve extrapolation approximates adopant depth of 4.5 μm.

The aluminum concentration at the wafer surface is approximately 2×1021cm-3 and decreases to about 1.5×1020 cm-3 at a depth of approximately1100 nm. Curve extrapolation approximates a dopant depth to be about 4.3μm.

The values of diffusion coefficients for nitrogen and aluminum dopantsare found to be 7×10-7 cm2/s and 4×10-7 cm2/s respectively, which are atleast 5 orders of magnitude higher than the typical values of 5×10-12cm2/s for nitrogen and 3×10-14 cm2/s˜6×10-12 cm2/s for aluminum reportedin the literature.

In a preliminary study an optical phase was created inside a polishedsingle crystalline 4H—SiC substrate FIG. 5 with a high intensity laserbeam. This embedded laser-metallized optical phase was tested forreflectivity using a green laser (wavelength, λ=532 nm). Thereflectivity of both the laser-metallized and parent silicon carbidesubstrate were found to be 16% and 10% respectively. This is areflectance increase of 60% for 532 nm wavelength irradiation, at roomtemperature.

Epitaxial SiC surfaces (epilayers) provide sufficient reflectivity forsignal processing asshown in Table 2.

TABLE 2 Reflectivity of Wafer and Epitaxy 4H-SiC surfaces [1].Reflectivity (%) of two types of reflecting surfaces Lasers EpilayerSubstrate Nd:YAG (□ = 1064 nm) 20.6 15 Green laser (□ = 532 nm) 22.622.4

In this present invention the optical properties (reflectivity,transmission, absorption coefficient, refractive index and absorptionindex) of the parent 6H—SiC wafer and the laser synthesized embeddedstructures (e.g., n-type doped, p-type doped region and laser metallizedstructures) were calculated based on the transmitted (PT) and reflected(PR) powers measured at a laser wavelength of 1064 nm using intensitiesmuch less than those used in laser doping and laser metallization.

The reflectivity of laser synthesized embedded optical structures areincreased by 40%; the parent wafer has a reflectivity of 20% and thatfor the laser synthesized structures are about 28%. Accordingly thetransmission of the laser synthesized optical structures decrease toabout 9% compared to 60.5% of the parent wafer.

Table 3 lists the calculated absorption coefficients, refractive indexand absorption index for the parent 6H—SiC wafer and the laserfabricated embedded optical structures, all of which have been increased(particularly absorption coefficient and absorption index). Theabsorption index is three orders of magnitude larger compared to theparent wafer. In addition, reported absorption coefficients for 6H—SiCconventionally doped (e.g., ion implantation) do not exceed 200 cm-1[6]; these laser doping results are greater than a factor of 15 higher.

TABLE 3 Room Temperature Optical Properties for Laser Doped OpticalStructures in 6H-SiC measured at λ = 1064 nm Parent Laser doped Laserdoped Laser Optical properties 6H-SiC (n-type) (p-type) metallizationAbsorption 6.07 4.66 × 10³ 4.64 × 10³ 4.56 × 10³ coefficient (cm⁻¹)Refractive index 2.62 3.25  3.31  3.21  Absorption index 5.14 × 10⁻⁵0.039 0.039 0.039

These increases in absorption coefficient are probably related to theformation of a carbon rich composition formed by laser metallization.Laser irradiation raises the SiC surface to the peritectic reactiontemperature (Tp≈2800° C.) thermally decomposing the SiC into a molten Sisupersaturated with graphite. The change in the Si/C atomic ratio shiftsthe bandgap and therefore dramatically changes the absorptivity sincethe absorption is directly related to the bandgap.

Laser doping significantly increases the dopant concentration, comparedto conventional doping (e.g., ion implantation) and, therefore, thecorresponding effects of band filling, bandgap shrinkage and freecarrier absorption increase the absorption coefficient.

Optical structures exhibiting elements of both laser metallization(e.g., a degree of Si/C atomic ratio change from a 1:1 stoichiometry)and laser doping are predicted to have the highest absorptioncoefficient, as observed.

EXAMPLE II Embedded Optical Phases (Structures)

-   -   The laser beam can be focused within the SiC wafer. In addition,        an incident laser beam is transmitted through the top surface of        the 6H—SiC wafer and is focused by refraction in the SiC wafer        to a smaller beam diameter in effect increasing laser beam        intensity. This is a direct write process. Optical        interferometry roughness measurements showed no deterioration in        surface roughness of the embedded optical phase (e.g., a        reflector) created adjacent to the back surface after this mode        of laser metallization; consequently, no post anneal is        required.    -   The fact that the width of the laser written reflector is        smaller than the diameter of the incident focused laser beam is        surprising and is not anticipated by Snell's Law. A plausible        explanation is the activation of nonlinear absorption, which        leads to the onset of a self-focusing effect in SiC wafers on        the order of 443 μm thick.    -   The laser beam scanning for laser metallization and lsaser        doping can be controlled to create an embedded optical lense,        optical waveguide and optical concentrator.

EXAMPLE III Laser Synthesized Electro-Optical Device

-   -   A tunable optical filter is fabricated using laser synthesis        technologies; primarily the tools of laser metalization and        laser doping. An n-doped 4H—SiC substrate is irradiated with a        laser beam to create two laser-metallized tracks along the paths        of the laser beam. The original laser doped n-doped        semiconductor material remains unaffected by the laser beam        between these two tracks, resulting in the fabrication of a        metal-semiconductor-metal (MSM) device. The transmissivity of        infrared radiation through the semiconductor changes when        voltage is applied to the MSM through the tracks. This        observation makes it possible to use the MSM device as a tunable        optical filter. The observed property of the MSM device provides        a reconfigurable means of routing optical signals in three        dimensions. It can also be used as a switch.

These processes enable the use of wide bandgap semiconductors (WBGS),which have higher breakdown voltages and therefore can accommodatehigher voltages. A higher operational voltage (field) range allowsoptical property tunability over a larger electromagnetic wavelengthrange. For example, silicon shows tunability over 0.8 nm wavelengthrange (ref: N. Duovich et al, IEEE, J. Quantum Electron, 37, 1030-1039(2001). Gallium Arsenide shows a tunablility range over 200 nm (ref:Website: Semiconductor Optoelectronic Device (Winter 2002).

Silicon carbide shows a tunability range >1850 nm as demonstrated fromour preliminary experiments where we applied a maximum voltage of 9V.This tunability range can be further increased with increase in appliedvoltage, say to 50V since wide bandgap semiconductors can toleratehigher breakdown voltages than either silicon or gallium arsenide (Table4.).

TABLE 4 Semiconductor Properties Gallium 6H Silicon Property SiliconArsenide Carbide Band Gap 1.12 eV 1.424 eV 3 eV Breakdown field 0.3MV/cm 0.4 MV/cm 3 MV/cm Dielectric constant 11.7 12.9 10 Thermal 1.3W/K-cm 0.55 W/K-cm 5 W/K-cm Conductivity Saturated electron 1 × 10⁷cm/sec 1 × 10⁷ cm/sec 2 × 10⁷ cm/sec drift velocity

The approach relies on the fact that the optical properties of n-type4H—SiC are controlled by its free carrier concentration. Laser directmetallization is used to fabricate metal-like contacts in situ in n-type4H—SiC (˜5×1019 cm-3) substrates generating aconductor-semiconductor-conductor structure as shown in FIGS. 7 and 9.Here, Δ% Transmission=(% transmission at a biasing voltage V−%Transmission at zero bias). Application of a biasing voltage (eitherforward or reverse) between the two contacts in this structure affectsthe optical transmissivity of the n-type SiC semiconductor.

FIG. 8 shows that the transmission increases as the magnitude of theapplied voltage increases over the wavelength range 1000-3000 nm at anapplied bias of 5-9 volts. Measurements were taken from 350 nm. Thedifference between the maximum and minimum values increases with theapplied bias.

These results indicate that the laser-metallized SiC can act as atunable optical filter in the infrared regime. The origin of thetunability is related to the free carrier absorption phenomenon, i.e.,the free carrier response to the incident electromagnetic field (at theJR wavelength) in the presence of the biasing voltage or the electricfield. Originally, when the sample is under no external bias the opticaltransmission at a given photon energy smaller than the bandgap iscontrolled by both the sub-bandgap transition and free carrierabsorption. An applied bias can deplete a given donor level by sweepingits electronic carriers to the conduction band. This decreases thecontribution of the sub-bandgap transition to the overall absorption atthe corresponding wavelength. The free carriers swept to the conductionband increase the contribution of the free carrier absorption at ahigher wavelength (i.e., lower frequency). Such behavior is responsiblefor the appearance of the maximum and minimum values in the transmissionspectrum. The maximum corresponds to the wavelength with photon energyequal to the difference between the depleted donor level and theconduction band edge. On the other hand, the minimum value, obtained ata higher wavelength, has a particular value which depends on the dopantconcentration and the density of states in the conduction band at agiven temperature. It should be noted that the above-mentioned tunableoptical response is only observed for SiC single crystal doped withdonor concentration higher than 1019 cm-3. The application of a biasingvoltage to a laser doped SiC wafer with laser metallized electrodes withdopant concentration lower than 1019 cm-3 did not reveal such a tunableresponse.

This example III demonstrates that photonic devices (e.g., waveguides,lenses, concentrators, etc.) exhibiting dynamically changing opticalproperties resulting from a change in biasing voltage can be fabricatedby the combination of laser doping and laser metallization. Further,this example III demonstrates that the combination of laser doping andlaser metallization can be used to fabricate integrated electronic andphotonic devices and, therefore, electro-optic, opto-electric, andintegrated electronic-photonic circuits.

FIG. 11 is a diagram of the first embodiment of the optical device 10being used for measuring temperature. In this example, the opticaldevice 10 is formed as an optical temperature sensor device 10E. Theoptical temperature sensor device 10E is suitable for measuringtemperature in a remote location 81 from an ambient location 82.

In this example, the remote location 81 is shown as a closure 90 havingan opening 92 communicating the ambient 82. A transparent window 94 ispositioned within the opening 92 by a mounting 96.

Although the remote location 81 has been shown as a closure, it shouldbe understood that the remote location 81 may be any type of remotelocation. A few examples of the remote location 81 include chemical,mechanical and nuclear combustors, reactors and chambers as well asearth, planet and space locations, and biological species locations.

The optical temperature sensor device 10E is formed within thewide-bandgap semiconductor substrate 20E as previously described withreference to FIGS. 1 and 2. The wide-bandgap substrate semiconductorsubstrate 20E has a first and a second substrate surface 21E and 22E.The optical temperature sensor device 10E includes a first and a secondoptical surface 11E and 12E.

The wide-bandgap semiconductor substrate 20E is positioned within theremote location 81 with the first surface 11E of the optical temperaturesensor device 10E facing the transparent window 94.

An interrogating laser 100 projects an incident laser beam 101 through apolarizing filter 104 and a beam splitter 106. The incident laser beam101 projects through the transparent window 94 to irradiate upon theoptical temperature sensor device 10E. For oblique incidence, thereflected power was measured without the beam splitter 106.

The first and second surfaces 11E and 12E of the optical temperaturesensor device 10E reflect the incident laser beam 101 as reflectedradiation 102. The beam splitter 106 reflects the reflected radiation102 to impinge upon a detector 110. The output of the detector 110 isconnected to a power meter 112 and a computer 114 for data analysis andprocessing.

The incident laser beam 101 irradiating upon the optical temperaturesensor device 10E is a coherent light beam. Although it should beunderstood that various light sources may be used to interrogated theoptical temperature sensor device 10E, a continuous wave He—Ne laseroperating at a wavelength of 632.8 nm has been found to be suitable forthe practice of this invention.

The reflected radiation 102 from the first and second surfaces 11E and12E of the optical temperature sensor device 10E forms interferencepattern (not shown) that impinges on the detector 110. The output of thedetector 110 is analyzed by a power meter 112 and a computer 114 todetermine the temperature of the remote location 81. A more detailedexplanation of the process the data from the detector by the power meterand the computer is set forth hereinafter.

FIG. 12 is a diagram of the second embodiment of the optical device 10Abeing used for measuring pressure and/or chemical composition. In thisexample, the optical device 10 is formed as an optical sensor device10F. The optical sensor device 10F is suitable for measuring pressureand/or chemical composition in a remote location 81 from an ambientlocation 82.

In this example, the remote location 81 is shown separated by a ambient82 by a wall closure 91 having an opening 93. It should be understoodthat the remote location 81 may be any type of remote location asheretofore described.

The optical sensor device 10F is formed within the wide-bandgapsemiconductor substrate 20F as previously described with reference toFIGS. 3-5. The wide-bandgap substrate semiconductor substrate 20F has afirst and a second substrate surface 21F and 22F. The optical sensordevice 10F includes a first and a second optical surface 11F and 12F.

The wide-bandgap semiconductor substrate 20F is secured within theopening 93 by a mounting 96. The wide-bandgap semiconductor substrate20F is positioned such that the first surface 11F of the optical sensordevice 10F is exposed to the ambient location 82 and facing theinterrogating laser 100. The wide-bandgap semiconductor substrate 20F ispositioned further to expose the second surface 12F of the opticalsensor device 10F to the remote region 81. Although the optical sensordevice 10F is shown located within the opening 93, it should beunderstood that the present invention is not limited to the specificphysical arrangement, location and mounting of the optical sensor device10F within the remote region 81.

An interrogating laser 100 projects an incident laser beam 101 through apolarizing filter 104 and a beam splitter 106. The incident laser beam101 irradiates upon the optical sensor device 10F.

The first and second surfaces 11F and 12F of the optical sensor device10F reflect the incident laser beam 101 as reflected radiation 102. Thebeam splitter 106 reflects the reflected radiation 102 to impinge upon adetector 110. The output of the detector 110 is connected to a powermeter 112 and a computer 114 for data analysis and processing.

The incident laser beam 101 irradiating upon the optical sensor device10F is a coherent light beam. Although it should be understood thatvarious light sources may be used to interrogated the opticaltemperature sensor device 10F, a continuous wave He—Ne laser operatingat a wavelength of 632.8 nm has been found to be suitable for thepractice of this invention.

The reflected radiation 102 from the first and second surfaces 11F and12F of the optical sensor device 10F forms interference pattern (notshown) that impinges on the detector 110. The output of the detector 110is analyzed by a power meter 112 and a computer 114 to determine thetemperature of the remote location 81.

A continuous wave He—Ne laser operating at a wavelength of 632.8 nm isused as the probe beam to interact with the SiC sensor remotely as afunction of temperature. The reflected power is measured with an opticalpower detector connected to a power meter. The data collection processis computerized to provide accurate value of temperature and power. Boththe reflected power and temperature are collected in a time-synchronizedmanner by using the computer. The optical response of the sensor isevaluated for defined incident angles of (0°) and (45°). For normalincidence, the beam is partially transmitted through the beam splitterplaced at 45° angle with respect to the incident beam. The beam splitterwas specifically designed to operate at 632.8 nm wavelength. A fractionof this beam is reflected and transmitted by the sensor.

FIG. 14 is a graph illustrating the reflected power for a sample A as afunction of temperature from 27° C. to 750° C. for a zero degree (0°)and a forty-five degree (45°) incidence angle.

FIG. 15 is a graph illustrating the reflected power for sample B as afunction of temperature from 27° C. to 750° C. for a zero degree (0°)and a forty-five degree (45°) incidence angle.

FIG. 16 is a graph illustrating a typical oscillatory reflected powerprofile commonly referred to as a complementary Airy pattern showing thephase angles between the adjacent branches of the oscillations.

FIG. 17 is a graph of the refractive index for sample A and B, from 27°C. up to 750° C., for 0° and 45° incidence angle.

FIG. 18 is a graph illustrating the concentration depth profiles ofAluminum and Nitrogen measured with SIMS for sample A.

FIG. 19 is a graph illustrating the concentration depth profiles ofAluminum and Nitrogen measured with SIMS for sample B.

FIG. 20 is a graph illustrating the reflectivity plot for sample A andB, as a function of temperature from 27° C. up to 750° C. for 0° and 45°incidence angle.

FIG. 21 is a graph illustrating the thermo optic coefficient for sampleA and B from 27° C. up to 750° C. for 6H silicon carbide (SiC) for 0°and 45° incidence angle and literature value for 6H silicon carbide(SiC) at 1.5 micro meter wavelength.

FIG. 22 is a graph illustrating the reflected power for laser-metallizedsample as a function of temperature for normal incidence of a He—Nelaser beam of power incident on a substrate the wafer is 6.7 mW.

Analytical Program

Several sets of the reflected power were measured for each of thelaser-doped samples A and B in accordance with the doping profile inFIGS. 18 and 19. A representative set is presented in FIGS. 14 and 15,respectively. The measured reflected power has definite oscillatorypatterns as a function of the sensor temperature as indicated in FIGS.14A 14B. The type and a mount of dopant atoms present in the SiC waferand thickness may also affect the nature of the patterns. Since bothsurfaces of the samples were polished, a portion of the beam transmittedthrough the top surface of the sample is reflected by the inner bottomsurface and this reflected light undergoes multiple reflections insidethe sample, i.e., within the thickness of the sample. At each reflectionpoint, a portion of the beam transmits through the top surface and thesetransmitted beams interfere to form the observed oscillatory pattern. Onthe other hand, the actual scattered power is obscured by theseoscillations, hindering the exact evaluation of reflectivity using themeasured power data because such data contain the effects of multiplereflections and the power of the specular reflected light. Due to theoscillatory patterns, the standard deviation in the estimated reflectedpower as a function of temperature becomes large. The phase angles ofthe interference fringes, which are manifested through the oscillatorypatterns as a function of temperature FIGS. 14A and 14B can be used toextract the refractive index and thermo-optic coefficient by consideringthat the wafer is inherently a Fabry-Perot etalon where the top andbottom surfaces of the sample serve as reflecting surfaces.

Refractive Index Analytical Program

The optical properties of the sensor were calculated using theoscillatory reflected power (P_(R)) obtained as a function of the sensortemperature for a defined incident angle. For the case of multiplereflections, the reflected light intensity pattern is given by thefollowing complementary Airy function

$\begin{matrix}{\frac{I_{r}}{I_{i}} = \frac{F\;\sin^{2}\phi}{1 + {F\;\sin^{2}\phi}}} & (1)\end{matrix}$where I_(i) is the incident flux density, I_(r), the reflected fluxdensity, F is the coefficient of finesse given by F=[2√{square root over(R)}/(1−R)]², R is the reflectance of the sample. The phase angle □ ofthe interference fringes (oscillatory pattern of the reflected power inthis study) is given by φ=2πn_(s) d/λ₀, where n_(s) is the refractiveindex of the sample (silicon carbide), d is the thickness of the sampleand λ₀ is the wavelength of the incident light in vacuum. Noting thatn_(s) and d vary with temperature, the variation of □ with respect totemperature can be obtained as follows by using the above expression for{tilde over (□)}

$\begin{matrix}{\frac{\partial\phi}{\partial T} = {{{\frac{2\pi\; d}{\lambda_{o}}\frac{\partial n}{\partial T}} + {\frac{2\pi\; n}{\lambda_{o}}\frac{\partial d}{\partial T}}} = {\frac{2\pi\; d}{\lambda_{o}}\left( {\frac{\partial n}{\partial T} + {\alpha\; n}} \right)}}} & (2)\end{matrix}$where

${\alpha = {\frac{1}{d}\frac{\partial d}{\partial T}}},$which is the thermal expansion coefficient of the wafer. Its value for6H—SiC is given byα=3.19×10⁻⁶+3.60×10⁻⁹ ×T−1.68×10⁻¹² ×T ²  (3)in the unit of K⁻¹, where T is the sensor temperature in Kelvin. Thephase shift of the reflected wave between any two adjacent maximum andminimum reflected powers is π. Let P_(m) and P_(m+1) be two suchadjacent data points as shown in FIG. 15. The refractive index andtemperature of the sensor corresponding to these two data points aren_(m), T_(m) and n_(m+1), T_(m+1) respectively such that T_(m+1)>T_(m).Assuming the curve to be linear between the points P_(m) and P_(m+1) inthe oscillatory pattern and applying the central finite differenceapproximation to (2) at the midpoint of this straight line, anexpression for n_(m+1) can be obtained as follows

$\begin{matrix}{n_{m + 1} = {{\frac{1}{1 + \frac{\alpha_{mid}\Delta\; T}{2}}\left\lbrack {\frac{\lambda_{0}}{2d} + {\left( {1 - \frac{\alpha_{mid}\Delta\; T}{2}} \right)n_{m}}} \right\rbrack}.}} & (4)\end{matrix}$Here □_(mid) is the thermal expansion coefficient of the sensor materialat the temperature corresponding to the midpoint (P_(mid)) of thestraight line P_(m)P_(m+1) in FIG. 15,

${i.e.},{\alpha_{mid} = {{{\alpha\left( \frac{T_{m} + T_{m + 1}}{2} \right)}\mspace{14mu}{and}\mspace{14mu}\Delta\; T} = {T_{m + 1} - {T_{m}.}}}}$Knowing the refractive index (n₀) of SiC at room temperature (T₀), therefractive indices can be obtained at higher temperatures by using (4).Examples of Refractive Index Analytical Program

Experiments were carried out to obtain the values of n0 for samples Aand B. The powers of the He—Ne laser beam reflected by and transmittedthrough each of the samples were measured at room temperature (T0).Based on these data, the refractive index (n0) and absorption index (k0)were calculated by using the Fresnel reflection formula, Beer-Lambertlaw and the relationship between the absorption coefficient andabsorption index. For normal incidence, the values of n0 and k0 werefound to be 2.596±0.247 and (7.448±0.331)×10-5, and 2.416±0.266 and(6.739±0.318)×10⁻⁵ for samples A and B respectively. Similarly for 45°angle of incidence, the values of n₀ and k₀ were found to be 2.633±0.483and (3.913±0.322)×10⁻⁵, and 2.499±0.447 and (3.540±0.322)×10⁻⁵ forsamples A and B respectively. Now, (4) can be applied to obtain therefractive index at higher temperatures. However, (4) needs to beimplemented over each branch of the oscillation in each cycle, i.e., nneeds to be calculated as n₁ for temperature T₁, n₂ for temperature T₂and so on. Here the temperature difference, e.g., T₂−T₁ or T₃−T₂, shouldbe on the same branch within each cycle as shown in FIG. 3. Therefractive indices are plotted in FIG. 16 as a function of temperature.The refractive indices for oblique incidence are slightly higher thanthat for normal incidence, which may be due to the crystal structure of6H—SiC polytype. 6H—SiC is a uniaxial, anisotropic crystal and therefractive index of such materials varies with the incident angle. Thistype of material will have varying refractive index lying between twoextrema corresponding to the refractive indices obtained for lightstraveling along the c^(⊥) or c^(∥) axis of the crystal. The prior artreported refractive indices 2.63 and 2.67 along C^(⊥) and c^(∥) axesrespectively for 6H—SiC at room temperature, confirming that therefractive index depends on the orientation of the crystal latticerelative to the incident light.

The refractive indices of the two samples are also different as shown inFIG. 16. This difference may be due to the differences in their dopant(both n- and p-type dopants) concentrations as shown in FIGS. 5 and 6for samples A and B respectively. The effect of dopant concentrations onthe refractive index is given by the following expression [23]-[25]

$\begin{matrix}{{\Delta\; n} = {{- \frac{{\mathbb{e}}^{2}\lambda_{0}^{2}}{8\;\pi^{2}c^{2}n_{u}ɛ_{0}}}\left( {{N_{e}/m_{ce}^{*}} + {N_{h}/m_{ch}^{*}}} \right)}} & (5)\end{matrix}$which is based on a free carrier model. Here □n=n_(u)−n, n_(u) and n arethe refractive indices of undoped and doped wafers respectively, e isthe electronic charge, λ₀ is the optical wavelength in vacuum, N_(e) isthe free electron concentration pertaining to the n-type dopant atoms,N_(h) is the free hole concentration pertaining to the p-type dopantatoms, m*_(ce) and m*_(ch) are the conductivity effective masses ofelectrons and holes respectively. Equation (5) was derived under theapproximations that □²□²>>1 and the square of absorption index isnegligible compared to the square of refractive index, where □=2c/□ and□ is the relaxation time of free carriers. These approximations holdgood for silicon in the wavelength range of 1.2 to 1.8 □m. In thepresent case of SiC samples, the absorption indices have been notedabove as negligibly smaller than the refractive indices. Also in thevisible wavelength of the He—Ne laser, □²□² would be much larger thanunity. Therefore (5) can be applied to the silicon carbide samples A andB to indicate that their dopant concentrations affect their refractiveindices.

Based on curve-fits, the variation of the refractive index withtemperature is given by the following expressions were □=the incidentangle:

Sample A:n=2.59+3.84×10⁻⁵ ×T+1.84×10⁻⁸ ×T ²+7.07×10⁻¹² ×T ³ for □_(i)=0°  (6a)n=2.63+2.2×10⁻⁵ ×T+7.07×10⁻⁸ ×T ²−3.16×10⁻¹¹ ×T ³ for □_(i)=45°  (6b)Sample B:n=2.41+5.61×10⁻⁵ ×T+3.18×10⁻⁸ ×T ²+5×10⁻¹² ×T ³ for □_(i)=0°  (7a)n=2.49+4.89×10⁻⁵ ×T+1.62×10⁻⁸ ×T ²+1.23×10⁻¹¹ ×T ³ for □_(i)=45°  (7b)Reflectivity Analytical Program

For the randomly polarized laser beam in this study, the beam wasassumed to consist of 50% perpendicular component and 50% parallelcomponent. The calculated net reflectivity (R) is the contribution ofthese components as given below.R=0.5×R _(TE)+0.5×R _(TM)  (8)For normal incidence, the reflectivity can be approximated by thefollowing expression:

$\begin{matrix}{R = \frac{\left( {n_{s} - 1} \right)^{2}}{\left( {n_{s} + 1} \right)^{2}}} & (9)\end{matrix}$

Based on the refractive indices given by 6(a, b) and 7(a, b), thereflectivities of samples A and B were calculated as a function oftemperature as presented in FIG. 19. Based on curve-fits, the variationof the reflectivity with temperature is given by the followingexpressions:

Sample A:R=19.61+5.27×10⁻⁴ ×T+2.52×10⁻⁷ ×T ²+9.24×10⁻¹¹ ×T ³ for □_(i)=0°  (10a)R=22.97+1.38×10⁻⁴ ×T+1.10×10⁻⁶ ×T ²−6.17×10⁻¹⁰ ×T ³ for □_(i)=45°  (10b)Sample B:R=17.09+7.97×10⁻⁴ ×T+4.50×10⁻⁷ ×T ²+6.26×10⁻¹¹ ×T ³ for □_(i)=0°  (11a)R=21.4+5.52×10⁻⁴ ×T+1.57×10⁻⁷ ×T ²+1.73×10⁻¹⁰ ×T ³ for □_(i)=45°  (11b)Thermo-Optic Coefficient Analytical Program

Thermo-optic coefficient (dn/dT), which is the rate of change ofrefractive index with temperature, was obtained by taking the derivativeof the third order polynomial fit of refractive index as a function oftemperature. This factor is important in optoelectronic deviceapplications such as switches, modulators and filters. The thermo-opticcoefficients of optical materials are generally in the range of 10⁻³ to10⁻⁵. The data reported in the prior art for 6H—SiC at 1.5 □m have alsobeen plotted along with the results of this study in FIG. 19. Thethermo-optic coefficients are approximately 10⁻⁵° C.⁻¹ for both samplesA and B. The thermo-optic coefficient is the derivative of refractiveindex and, therefore, it is very sensitive to the changes in refractiveindex with respect to temperature. Small errors due to averaging andcurve fitting may influence the derivate, i.e., the thermo-opticcoefficient. This can be observed in FIG. 19 as the data for sample Afollow a different trend at both the normal and oblique incident angles,whereas the data are found to be similar for sample B.

Laser Metallization to Create Monotonic Response

In FIGS. 14 and 15, the reflected powers are oscillatory, i.e.,multi-valued functions of temperature. In other words, the opticalresponses in these two figures are not monotonically increasing ordecreasing functions of temperature. Therefore such data cannot be useddirectly to measure temperature by using SiC as a thermal sensor inpractical applications. To obtain a better optical response that can beused directly for temperature measurement, the microstructure insidesample A was modified by irradiating the sample with a high intensityNd:YAG pulsed laser beam (average laser power=2.5 W, pulse repetitionrate=5 kHz, beam radius at the surface of the sample=45 to 55 □m withthe laser focal spot being 5 mm above the top surface of the sample,laser beam scanning speed=1 mm/s) in the presence of argon gas at 30 psipressure. This process is known as laser metallization in whichlocalized heating by the high intensity laser beam disorders thecrystalline structure of SiC and produces carbon-rich phases whichusually exhibit metal-like properties. The laser parameters were chosenproperly to modify the microstructure inside sample A. The opticalresponse of this laser-metallized sample was obtained as a function oftemperature for the He—Ne laser as presented in FIG. 18, which showsthat the oscillations of the reflected power are negligibly smallcompared to the oscillations in FIGS. 14 and 15. Due to this, thereflected power in FIG. 18 can be considered as a monotonic function oftemperature.

FIG. 23A is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 14.7 psi.

FIG. 23B is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 100 psi.

FIG. 23C is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 200 psi.

FIG. 23D is a graph illustrating reflected power of a silicon carbidesensor upon exposure to nitrogen gas at a pressure as a function oftemperature at a pressure of 400 psi.

FIG. 24A is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 14.7 psi.

FIG. 24B is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 100 psi.

FIG. 24C is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 200 psi.

FIG. 24D is a graph illustrating reflected power of a silicon carbidesensor upon exposure to argon gas at a pressure as a function oftemperature at a pressure of 400 psi.

FIG. 25 is a graph of the refractive index of silicon carbide sensorwhen exposed to nitrogen as a function of temperature at pressures of14.7 psi, 100 psi, 200 psi and 400 psi.

FIG. 26 is a graph of the refractive index of silicon carbide sensorwhen exposed to argon as a function of temperature at pressures of 14.7psi, 100 psi, 200 psi and 400 psi.

FIG. 27 is a graph of the refractive index of a composite layer uponexposure to Nitrogen as a function of temperature at pressures of 14.7psi, 100 psi, 200 psi and 400 psi.

FIG. 28 is a graph of the refractive index of a composite layer uponexposure to argon as a function of temperature at pressures of 14.7 psi,100 psi, 200 psi and 400 psi.

FIG. 29A is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 14.7 psi.

FIG. 29B is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 100 psi.

FIG. 29C is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 200 psi.

FIG. 29D is a graph illustrating refractive index of the composite layersensor upon exposure to Nitrogen and Argon gas at a pressure as afunction of temperature at a pressure of 400 psi.

FIG. 30A is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 27° C.

FIG. 30B is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 100° C.

FIG. 30C is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 200° C. and

FIG. 30D is a is a graph illustrating refractive index of Nitrogen andArgon gas as a function of pressure at a temperature of 300° C.

TABLE 5 Fitting parameters a and b for determining the refractive indexof nitrogen and argon. Pressure 27° C. 300° C. Gas (psi) n₃ N n_(g) n₃ Nn_(g) a b Nitrogen 14.7 2.359 2.41618 1.00027 2.34623 2.43851 1.00014−0.5411 3.665 100 2.35 2.42312 1.00184 1.99335 2.44037 1.00096 −18.2946.602 200 2.3284 2.42593 1.00369 1.98377 2.44312 1.00193 −15.88 40.703400 2.29255 2.42885 1.00739 1.9718 2.44729 1.00387 −11.61 30.278 Argon14.7 2.2104 2.41202 1.00025 2.19345 2.43556 1.00013 −0.6876 3.8676 1002.20871 2.42020 1.00174 2.12064 2.43833 1.00091 −4.283 12.552 2002.19357 2.42206 1.00348 2.06 2.44020 1.00182 −5.872 16.360 400 2.179812.4251 1.00696 1.98027 2.44385 1.00364 −7.191 19.485

A helium-neon laser of wavelength 632.8 nm is used as a probe laser toobtain the complementary Airy pattern of the laser power reflected off asilicon carbide wafer segment at high temperatures (up to 300° C.) andpressures (up to 400 psi). The interference patterns revealed uniquecharacteristics for nitrogen and argon test gases. This pattern isdifferent at the same pressure and temperature for the two gases,indicating the chemical sensing capability of silicon carbide. Also thepattern changes with pressures for the same gas, indicating the pressuresensing capability. The refractive index of silicon carbide is obtainedfor different pressures and temperatures using the interference pattern.A three-layer model program using reflected radiation is used tocalculate the refractive indices of the gases.

Optical techniques such as multibeam interference have been used fortemperature measurement by interrogating a thin film of SiC (0.5-2 □m)on a single crystal sapphire, a Fabry-Perot cavity. The temperatureresponse of the sensor was evaluated up to 540° C. in the visible toinfrared wavelength region. In this study the optical response of asilicon carbide wafer segment has been detected in the form of acomplementary Airy pattern for two different gases for varyingtemperature and pressure. The SiC wafer segment is a Fabry-Perot etalon.The principle of multibeam interferometry has been applied to analyzethe patterns.

The reflected radiation is measured with an optical power detectorconnected to a power meter. A randomly polarized He—Ne laser beam isconverted to the transverse magnetic (TM) mode, i.e., a parallelpolarization component created by passing the beam through a polarizer.The beam splitter is specifically designed to operate at 632.8 nmwavelength. A fraction of this beam is reflected and transmitted by thesensor. The reflected beam is transmitted through the beam splitter ontoa detector that measures its power.

The power of the He—Ne laser beam reflected by the silicon carbidesubstrate exhibited oscillatory patterns FIGS. 23 and 24, which are dueto the constructive and destructive interferences of the reflectedlight. A portion of the incident beam is transmitted through the siliconcarbide wafer segment. This beam undergoes multiple reflections betweenthe top and bottom surfaces of the wafer segment, emerges asphase-shifted light through the top surface and interferes to producethe observed interference pattern. In FIGS. 23 and 24 the maximarepresents the constructive interference effect and the minima is thedestructive interference. The maxima correspond to the even multiples ofthe phase angle (□) and the minima correspond to the odd multiples of □.For normal incidence of the laser beam, the phase angle is given by

$\begin{matrix}{{\varphi = {2\pi\frac{{n\left( {\lambda,T,P} \right)}{d\left( {T,P} \right)}}{\lambda}}},} & (12)\end{matrix}$

where n(λ,T,P) is the refractive index of the optical sensing device10F, which is influenced by the wavelength (λ) due to the dispersionphenomenon, temperature (T) due to the thermo-optic effect and pressure(P) due to the stress-optics effect. d(T,P) is the sample thicknesswhich is affected by the temperature and pressure, and λ is thewavelength of the incident light in vacuum.

FIGS. 23 and 24 represent the reflected radiation of the optical sensingdevice 10F when the second surface 22F is exposed to nitrogen and argon,respectively, at varying pressures. The change in temperature at aconstant pressure causes the reflected radiation to oscillate betweencertain maximum and minimum values. These oscillations reveal aninteresting pattern. Unlike the cases of atmospheric pressure shown inFIG. 23A and FIGS. 24A, the oscillations tend to diverge progressivelywith temperature at higher pressures. The divergence patterns of theoscillations are unique to the type of gases, nitrogen and argon in thiscase, signifying that these patterns can be attributed to thecharacteristic identity of the individual gases in chemical sensingapplications. The optical sensor device 10F is selective to the gasspecies. Another aspect of these characteristic oscillations is that thedivergence pattern fans out with increasing pressure, thus enablingpressure sensing capability of the optical sensor device 10F.

Refractive Index Analytical Program for High Pressure and Temperature

The refractive index of the optical sensor device 10F can be obtainedfrom the above-mentioned interference pattern using the followingexpression

$\begin{matrix}{{n_{m + 1} = {\frac{1}{1 + \frac{\alpha_{mid}\Delta\; T}{2}}\left\lbrack {\frac{\lambda_{0}}{2{d\left( {T_{0},P} \right)}} + {\left( {1 - \frac{\alpha_{mid}\Delta\; T}{2}} \right)n_{m}}} \right\rbrack}},} & (13)\end{matrix}$where n_(m+1) and n_(m) are the refractive indices of optical sensordevice 10F at locations l_(m+1) and l_(m), i.e., at temperatures T_(m+1)and T_(m), respectively and at the pressure P that was applied to thewide-bandgap semiconductor substrate 20F using nitrogen or argon. Inother words, n_(m) can be written as n_(m)=n(T_(m),P) for a fixedwavelength. □_(mid) is the thermal expansion coefficient of wide-bandgapsemiconductor substrate 20F at the temperature corresponding to themidpoint (l_(mid)) of the straight line l_(m)l_(m+1) in. Its value forsilicon carbide is given byα=3.19×10⁻⁶+3.60×10⁻⁹ ×T−1.68×10⁻¹² ×T ².  (14)

${{So}\mspace{14mu}\alpha_{mid}} = {{{\alpha\left( \frac{T_{m} + T_{m + 1}}{2} \right)}\mspace{14mu}{and}\mspace{14mu}\Delta\; T} = {T_{m + 1} - {T_{m}.}}}$Knowing the refractive index (no) of SiC, which is calculated at roomtemperature (T₀) using Fresnel's formula R=(n−1)²/(n+1)², the refractiveindices can be obtained at higher temperatures from Eq. (2). While theeffect of temperature on the thickness of silicon carbide is consideredusing the thermal expansion coefficient, the effect of pressure on thethickness is taken into account using the expression d(T₀,P)=d₀(1−ε),where d(T₀,P) is the wafer segment thickness at room temperature (T₀)and pressure (P), whose values are approximately 412, 405 and 390 □m atthe gas pressures of 100, 200, and 400 psi respectively, d₀=420 □m whichis the original thickness of the wide-bandgap semiconductor substrate20F.

The strain (ε) is given by □=□/E, where σ is the applied stress and E isthe elastic modulus. The value of elastic modulus has been reported as392-694 GPa for 6H—SiC. In this study an average value of 543 GPa wasused for E and the stresses were taken to be 14.7, 100, 200, and 400psi.

FIGS. 25 and 26 illustrate the refractive index of the wide-bandgapsemiconductor substrate 20F increases with applied pressure. Theinterface of the wide-bandgap semiconductor substrate 20F and gas(nitrogen or argon) experiences compressive stresses under high gaspressures and this produces a comparatively denser layer of wide-bandgapsemiconductor substrate 20F near the second surface 22F. The refractiveindex of this compressed layer is higher than the refractive index ofthe overlying uncompressed layer. FIGS. 25 and 26 shows an increase inthe refractive index with pressure.

Three-Layer Program Model for the Effect of Gas Pressure on theRefractive Index of 6H—SiC

As mentioned above, the type of the gas and the pressure of the gasaffect the oscillatory pattern of the reflected light. To analyze thiseffect, a three-layer model is considered (inset in FIG. 1) in whichlayer 1 is the ambient air on top of the optical sensing device 10F,layer 2 is the optical sensing device 10F itself with refractive indexas determined above and layer 3 is a composite layer consisting of a fewcompressed atomic planes of the SiC crystal and a high pressure sheet(boundary layer) of the gas around the bottom surface of the wafer. Thereflectance, R, of such a three-layer structure can be expressed as²⁵

$\begin{matrix}{R = \frac{r_{12}^{2} + r_{23}^{2} + {2\; r_{12}r_{23}\cos\;\phi}}{1 + {r_{12}^{2}r_{23}^{2}} + {2r_{12}r_{23}\cos\;\phi}}} & (15)\end{matrix}$for a given laser beam, where r₁₂, and r₂₃ are the Fresnel reflectioncoefficients of layer 1-layer 2 and layer 2-layer 3 interfacesrespectively. Eq. 4 can be solved for r₂₃, which is given by

$\begin{matrix}{r_{23} = {\frac{{- \left( {\left( {1 - R} \right)r_{12}\cos\;\phi} \right)} \pm \sqrt{\left( {\left( {1 - R} \right)r_{12}\cos\;\phi} \right)^{2} - {\left( {1 - {Rr}_{12}^{2}} \right)\left( {r_{12}^{2} - R} \right)}}}{\left( {1 - {Rr}_{12}^{2}} \right)}.}} & (16)\end{matrix}$, and then the refractive index, n₃, of the composite layer is obtainedfrom the Fresnel relation expressing the refractive index in terms ofthe Fresnel reflection coefficient²⁵

$\begin{matrix}{n_{3} = {n{\frac{1 + r_{23}}{1 - r_{23}}.}}} & (17)\end{matrix}$

Eq. 5 yields two values of r₂₃, which in turn provide two values of therefractive index n₃. In this study, one of the two values was found tobe very close to the refractive index of SiC (e.g., 2.39) and the othervalue was very high (e.g., 17.44). So the actual refractive index n₃ wasselected to be the one that was within close proximity of the refractiveindex of SiC.

To calculate r₂₃ using Eq. (6), the reflectance data (FIGS. 2 and 3)were used and r₁₂ was determined using Fresnel's relationr₁₂=(n₂−1)/(n₂+1). The value of □ at any point on the complementary Airypattern was obtained through linear interpolation along each arm of thepattern (e.g., straight line l_(m)l_(m+1) in FIG. 4) and by noting thatthe maximum and minimum points in the pattern correspond to even and oddmultiples of π respectively. The refractive index of the composite layer(n₃) was obtained using Eq. 6 and its average values are shown in FIGS.7 and 8. As mentioned before, the composite layer is formed by theSiC-gas interface (inset in FIG. 1) and therefore the optical propertiesof this region are expected to be different from that of the gas. Alsothe refractive index of this composite region may be governed by thecomplex interactions of the atoms of SiC and gas at high temperaturesand pressures.

FIGS. 7 and 8 show that the refractive index of the composite layerdecreases with temperature. This trend suggests that the gas sheet ofthis composite layer has a dominant effect on the refractive index (n₃)of the composite layer when the temperature increases. This may occurbecause the refractive index of gases generally decreases as thetemperature increases. The decrease in the refractive index, however, ismuch less at atmospheric pressure than at higher pressures (100, 200 and400 psi). This effect of the pressure is associated with the divergencepatterns in FIGS. 2 and 3 where the oscillatory patterns exhibit littleor no divergence at atmospheric pressure compared to the patterns athigher pressures.

Refractive Index and Analytical Program for Gases at High Pressures andTemperatures

The refractive index of a gas, n_(g), is related to its density by thefollowing Gladstone-Dale relationn _(g)=1+R _(GD)ρ,  (18)where R_(GD) is the Gladestone Dale constant and ρ is the density of thegas. The values of R_(GD) are 0.238 and 0.158 cm³/g for nitrogen andargon respectively. Eq. (8) can be rewritten for an ideal gas asfollows.

$\begin{matrix}{{n_{g} = {1 + {R_{GD}\frac{PM}{R^{*}T}}}},} & (19)\end{matrix}$where M is the molecular weight of the gas, R* is the universal gasconstant and T is the absolute temperature of the gas. The theoreticalrefractive indices of the two gases obtained from Eq. (8) are plotted inFIG. 9, which also contains the refractive indices determined from theexperimental data. The refractive index for the gases is obtained byconsidering that the refractive index of the composite layer depends onthe refractive indices of SiC and gas linearly as given byn ₃ =a×n+b×n _(g),  (20)where a and b are two constants which are determined by fitting thedata, i.e., the values of n₃ and n (which are based on the experimentaldata) and the values of n_(g) (which are based on the theoreticalexpression (9)), at two different temperatures such as the roomtemperature and 300° C. These values are listed in Table I for nitrogenand argon respectively for different pressures. The refractive index ofthe gas was found to be inversely proportional to temperature anddirectly proportional to the pressure of the gas as predicted by thetheory. The refractive indices of nitrogen and argon are shown in FIG.10 as a function of pressure.

The reflectance of the optical sensing device 10F exhibited uniqueoscillatory patterns for both nitrogen and argon at high pressures andtemperatures. The oscillatory pattern tends to diverge with increase inpressure. This divergence is more prominent for argon than for nitrogen.These patterns are utilized to determine the refractive indices of SiCand the underlying gas in order to measure the pressure of the gas andto identify the type of the gas. At high pressures and temperatures,complex optothermal and optomechanical interactions occur between thegas and the compressed atomic planes of the SiC crystal, leading to theformation of a composite layer whose refractive index is different fromthat of the original optical sensing device 10F and the underlying gas.The refractive index of this composite layer is obtained using thereflectance data and then the refractive indices of the gases areobtained using an empirical relation involving the refractive indices ofthe composite layer and the optical sensing device 10F.

The present invention has several advantages over the prior art. Thepresent invention enables in situ processing results in no thermalcoefficient of expansion mismatch created when coatings are used.Annealing of the treated area is simultaneous, preventing defectgeneration. The scan rate may be modeled to increase with laserintensity. The invention utilizes commercially available optics definesgeometries. Doping can be selectively located by choice of laserparameters. Wide-bandgap semiconductor substrate impurities may be zonerefined or evaporated during processing. Wide-bandgap semiconductorsubstrate defects are annealed out during processing. Thelaser-converted phases are stable at high temperatures (950 C andabove). The converted phases can be are embedded improving chemicalstability. A polished single crystalline silicon carbide substrate orepitaxial surface shows sufficient chemical stability in oxygen up to1000° C. Laser conversion technology reduces process steps and reduceslattice and surface defect generation during processing. Optical andelectrical phases are created by the same process.

The present disclosure includes that contained in the appended claims aswell as that of the foregoing description. Although this invention hasbeen described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

1. A method for making an optical device within a wide-bandgapsemiconductor substrate, the method comprising, the steps of: providinga wide-bandgap semiconductor substrate defined between a first and asecond outer substrate surface; applying a doping gas to thewide-bandgap semiconductor substrate; and directing a laser beam onto aselected portion of the wide-bandgap semiconductor substrate locatedbetween the first and second outer substrate surfaces in the presence ofthe doping gas for changing an optical property of the selected portionto convert the selected portion of the wide-bandgap semiconductorsubstrate into the optical device.
 2. A method for making anelectro-optical device within a wide-bandgap semiconductor substrate,the method comprising, the steps of: providing a wide-bandgapsemiconductor substrate defined between a first and a second outersubstrate surface; applying a first doping gas to the wide-bandgapsemiconductor substrate; directing a first laser beam onto a firstselected portion of the wide-bandgap semiconductor substrate locatedbetween the first and second outer substrate surfaces in the presence ofthe first doping gas for changing an optical property of the firstselected portion to convert the first selected portion of thewide-bandgap semiconductor substrate into the optical device; applying asecond doping gas the wide-bandgap semiconductor substrate; anddirecting a second laser beam onto a second selected portion of thewide-bandgap semiconductor substrate located between the first andsecond outer substrate surfaces in the presence of the second doping gasfor changing an electrical property of the second selected portion toconvert the second selected portion of the wide-bandgap semiconductorsubstrate into the electrical device.
 3. A method as set forth in claim2, wherein the step of directing a second laser beam onto the secondselected portion includes converting the second selected portion into anelectrical conductor.
 4. A method as set forth in claim 2, wherein thestep of providing a wide-bandgap semiconductor substrate includesproviding a wide-bandgap semiconductor substrate having a bandgapgreater than 2.0 electron volts.
 5. A method as set forth in claim 2,wherein the step of providing a wide-bandgap semiconductor substrateincludes providing a wide-bandgap semiconductor substrate selected fromgroup IV of the periodic table and having bandgap greater than 2.0electron volts.
 6. A method as set forth in claim 2, wherein the step ofdirecting a laser beam includes directing a laser beam for defining theshape of the selected portion of the wide-bandgap semiconductorsubstrate.
 7. A method as set forth in claim 1, wherein the opticaldevice provides a changing optical reflectivity, a changingtransmission, a changing absorption coefficient, a changing refractiveindex and/or a changing absorption index.
 8. A method as set forth inclaim 2, wherein the step of directing a second laser beam onto thesecond selected portion includes converting the second selected portioninto an electrical conductor for creating a metal-semiconductor-metaldevice wherein transmission of electromagnetic irradiation through thesemiconductor region changes with change in applied voltage.
 9. A methodfor making an optical device within a wide-bandgap semiconductorsubstrate, the method comprising, the steps of: providing a wide-bandgapsemiconductor substrate defined between a first and a second outersubstrate surface; and directing a laser beam onto a selected portion ofthe wide-bandgap semiconductor substrate located between the first andsecond outer substrate surfaces for changing the stoichiometry of atomicelements within the selected portion of the wide bandgap semiconductorfor changing an optical property of the selected portion to convert theselected portion of the wide-bandgap semiconductor substrate into theoptical device.
 10. A method for making an optical device in a siliconcarbide wide bandgap semiconductor substrate, the method comprising, thesteps of: providing a silicon carbide wide-bandgap semiconductorsubstrate defined between a first and a second outer substrate surface;and directing a laser beam onto the silicon carbide wide-bandgapsemiconductor substrate located between the first and second outersubstrate surfaces for changing the stoichiometry of atomic elementswithin the silicon carbide wide bandgap semiconductor substrate tocreate a carbon rich phase region and a silicon rich phases regionhaving different optical properties.
 11. A method for making anelectro-optical device within a wide-bandgap semiconductor substrate,the method comprising, the steps of: providing a wide-bandgapsemiconductor substrate defined between a first and a second outersubstrate surface; applying a first doping gas to the wide-bandgapsemiconductor substrate; directing a first laser beam onto a firstselected portion of the wide-bandgap semiconductor substrate locatedbetween the first and second outer substrate surfaces in the presence ofthe first doping gas for changing an optical property of the firstselected portion of the wide bandgap semiconductor to convert the firstselected portion of the wide-bandgap semiconductor substrate into theoptical device; and directing a second laser beam onto a second selectedportion of the wide-bandgap semiconductor substrate located between thefirst and second outer substrate surfaces for changing the stoichiometryof atomic elements within the second selected portion of the widebandgap semiconductor for changing an electrical property of the secondselected portion to convert the second selected portion of thewide-bandgap semiconductor substrate into the electrical device.